Many building structure designs include the use of diagonal braces to provide lateral stability, especially for the purpose of increasing the lateral stiffness of the structure and reducing the cost of construction. In such bracing systems it is known that one or more sacrificial yielding fuse elements may be implemented in order to dissipate seismic input energy in the event of dynamic loading, such as during a severe seismic event. Such sacrificial yielding fuse elements are selected because they lead to improved seismic performance and reduced seismic loads when compared to traditional lateral load resisting systems.
For example, U.S. Pat. Nos. 6,530,182 and 6,701,680 to Fanucci et al. describe an energy absorbing seismic brace having a central strut surrounded by a spacer and sleeve configuration.
Similarly, U.S. Pat. Nos. 6,837,010 and 7,065,927 and U.S. Patent Application Publication No. 2005/0108959 to Powell et al. describe a seismic brace comprising a shell, containment member and a yielding core.
Brace apparatuses are also disclosed in U.S. Pat. No. 7,174,680 and U.S. Patent Application Publication No. 2001/0000840.
Most of these prior art systems require a buckling restraining apparatus used in conjunction with a yielding member, and are generally formed of steel plates and are not cast. Further, these prior art systems make use of axially yielding members, whereas it would be advantageous to use flexural yielding elements as they are less prone to fracture caused by excessive inelastic straining.
U.S. Pat. No. 4,823,522 to White, U.S. Pat. No. 4,910,929 to Scholl and U.S. Pat. No. 5,533,307 to Tsai and Li all describe steel yielding fuse elements that are placed at the centre of a beam and are used to add damping and stiffness to a seismically loaded moment resisting frame. The damping elements are generally formed with steel plates that are cut into triangular shapes and welded or bolted to a rigid base. Also, these elements are generally installed at the centre of the upper brace in and inverted V-type braced frame. Thus the yielding of these elements is controlled by the inter-story displacement of the frame. However, a yielding element that was linked to the brace elongation rather than the inter-story displacement would integrate more easily with current construction practices.
Another prior art fuse system, the EaSy Damper, uses a complex fabricated device to improve the seismic performance of brace elements by replacing axial yielding and buckling of the brace with combined flexural and shear yielding of a perforated, stiffened steel plate. The shapes of these plates do not result in constant curvature of the yielding elements and thus lead to undesirable strain concentrations.
Both of the aforementioned prior art systems require painstaking cutting and welding fabrication. Furthermore, the limited geometry of currently available rolled steel products restricts the potential geometry of the critical yielding elements of such devices.
Having greater control of the geometry of the flexural yielding elements permits control of not only the force at which the fuse yields, but also the elastic and post yield stiffnesses of the fuse as well as the displacement associated with the onset of fuse yielding. With casting technology a better performing fuse can be designed and manufactured. Also, free geometric control would enable the design of a part that would more easily integrate with existing steel building erection and fabrication practices than the prior art.
In view of the foregoing, an improved yielding fuse member for dynamic loading applications is desirable.